Preparation of alkylnaphthalene concentrates



March 9, 1965 P. F. HAGERTY ETAL 3,172,919

PREPARATION OF ALKYLNAPHTHALENE CONCENTRATES Filed June 8, 1961FPrifmonI Raffinate U Ul' r a :2 Phase lst Ehxtract l9 Feed .J l P use,Reject Phase IO l3 i l Secondary Furfural 2nd Extract Hexflne PhaseSecondary Furfural R ject Phase lsf Extract Phase 2nd Extract Hexane J Iphase INVENTORS P. FRANK HAGERTY ESAROLD F. TSE Br. JAY SURRENA ATTORNEYUnitd States 3,172,919 PREPARATEUN F ALKYLNAPHTHALENE C(DNCENTRATES Thisinvention relates to the preparation of alkylnaphthalene concentrateswhich are suitable feed stocks for conversion to naphthalene by hightemperature dealkylation.

Gas oils derived from hydrocarbon cracking processes which are eitherthermal or catalytic are composed generally of non-aromatichydrocarbons, monocyclic aromatics and dicyclic aromatics. The latterare mainly alkylnaphthalenes such as mono-, di-, andtrimethylnaphthalenes and, in smaller quantity, the ethylnaphthalenes.The aromatic hydrocarbon content of cracked gas oils usually lies Withinthe range of 30-80% by volume with the amount depending upon theparticular operation in which the gas oil has been produced.

It is known that naphthalene can be produced from the alkylnaphthalenesby high temperature dealkylation in the presence of hydrogen. Processesfor effecting this reaction non-catalytically generally require atemperature in the range of 1200-1400 F. When a catalyst such as cobaltmolybdate is used, a somewhat lower temperature can be employed, forexample, ll00l200 F. In utilizing cracked gas oil as a source of alkylaromatics for feed to such dealkylation processes, a problem ispresented in the preparation of a suitable alkylnaphthalene concentrateas feed stock. It is important that the feed have a low content ofnon-aromatics as well as a reduced content of monocyclic aromatics, forthe reason that these components crack rapidly at the high temperatureemployed and a highly exothermic reaction is encountered. The presenceof substantial amounts of these components which are not precursors fornaphthalene formation, and particularly the presence of thenon-aromatics, tends to make the reaction uncontrollable. For theprocess to operate properly, it is highly desirable that the feed be adicyclic aromatic concentrate and that it contain as low a content ofnon-aromatics as possible.

The present invention provides an economical procedure for processingcracked gas oil to produce dicyclic aromatic concentrates which areparticularly suitable as feed to such dealkylation operations. Accordingto the invention, a fraction derived from cracked gas oil and boilingmainly in the range of 440l5 F. is first countercurrently extracted witha furfural solvent in limited amount but suflicient to extractessentially all of the dicyclic aromatics. Most of the non-aromatics anda portion of the monocyclic aromatics remain in the raffinate phase andare removed. The extract phase contains essentially all of the dicyclicaromatics, a major part of the monocyclic aromatics and also asubstantial but minor amount of the non-aromatics. The extract phase isthen treated with a C C saturated hydrocarbon, such as hexane, in amanner whereby essentially all of the non-aromatics and a portion of themonocyclic aromatics are displaced therefrom, being replaced by the C Csaturated hydrocarbon. However, prior to such treatment it is essentialthat the extract phase be diluted with more furfural solvent Within alimited proportion range as hereinafter specified. Omission of thisdilution step will vitiate the treatment with the C -C saturatedhydrocarbon and result in failure to achieve the desired displacement ofthe non-aromatics. By first diluting with atent furfural in the properamount and then treating with hexane in proper amount, a product can beobtained which contains nearly all of the dicyclic aromatics andessentially none of the non-aromatics'that were present in the feed.This product is eminently suitable for conversion to naphthalene by hightemperature dealkylation.

The invention is more specifically described with reference to theaccompanying drawing in which FlGURE 1 is a schematic illustration ofone embodiment of the invention and FIGURE 2 is a schematic illustrationof another embodiment.

Referring first to FIGURE 1, a feed stock derived from catalytic gas oiland having a boiling range of 440515 F. and an aromatic content'of, forexample, 54% by volume is introduced through line 10 into the bottom ofa countercurrent contactor 11. Furfural solvent, herein referred to asprimary furfural, is introduced to the top of the columnthrough line 12and flows downwardly therein countercurrent to the feed. The termfurfural solvent as used herein refers to furfural itself or furfuralcontaining dissolved water in any amount up to saturation at thetemperature of the extraction operation. Column 11 should be operated ata temperature in the range of 10150 F. and more preferrably l10 F. Inthis operation-it is important that the amount of primary furfural fedtothe column be such that, on a volume basis, its ratio to the totalaromatics in the feed lies in the range of 0.75:1 to 7:1 and morepreferably 1:1 to 2:1. Under these conditions the extract phase, whichis withdrawn from the column through line 13 and is herein referred toas the 1st extract phase, will contain essentially all of the dicyclicaromatics, while the raifinate phase, which is removed via line 14, willcontain a major proportion of the non-aromatics and some of themonocyclic aromatics The 1st extract phase in line 13 is admixed with anappropriate amount of additional furfural solvent, herein referred to assecondary furfuraljfed through line 15, and the mixture is sent to thetop of a second column 16. It is important'that the amount of secondaryfurfural used be in the range of 0.15 to 2.5 volumes-per volume ofextract (i.e., gas oil hydrocarbons) in the extract phase and morepreferably in the range of 0.25 to 1.25 vols/vol.

A C C saturated hydrocarbon or mixture of such hydrocarbons is fed tothe bottom of column 16 through line 17 and therein passes upwardly incontact with the downfiowing extract phase. Any parafiinic or naphthenicC C hydrocarbon or mixture'thereof can be used for this purpose. The C-C hydrocarbon material can contain a minor amount, for example, up to10% by volume of aromatic components such as benzene and toluene. In thepresent description hexane will be considered as the saturatedhydrocarbon employed. Again,

it is important that the amount of hexane be regulated within a specificrange, namely, from 0.5 to 2.0 vols. per vol. of extract in the 1stextract phase fed to the top of column 16. More preferably, this ratiois in the range of 0.751.1 vols/vol. The temperature of this operationcan be in the range of 1015()" F., more'preferably 70ll0 F., and it mostpreferably is about the same as the temperature used for the extractionin column 11. Contact of the hexane in the amount specified with the 1stextract phase causes most of the hexane to dissolve in the furfural anddisplace the non-aromatics therefrom along with a part of the monocyclicaromatics. There is Withdrawn from the top of the column through line 19a reject phase which contains essentially all of the nonaromatics thatwere present in the 1st extract phase and only a small amount of thehexane used. From the base of the column a 2nd extract phase is removedthrough line 18. This material contains nearly allof the dicyclicaromatics that were present in. the feed, generally less than 50% of themonocyclic aromatics that were present and essentially none of thenon-aromatics.

To illustrate the operation of the process more specifically, data aretabulated below to show a material balance (weight basis) for anoperation in which it is assumed that 100 lbs. of gas oil feed fraction,116 lbs. of primary furfural, 59.2 lbs. of secondary furfural and 35.3lbs. of hexane are introduced per unit time. Each column is a contactorof the rotating disc type and is operated at a temperature ofapproximately 100 F.

From the data tabulated, it can be seen that, upon distillation of the2nd extract phase to remove hexane and furfural, the extract productobtained will be composed of about 65 dicyclic aromatics and 35%monocyclic aromatics. It can also be seen that only about 13% of thehexane used appears in the reject phase. Hence the operation in column16 is mainly not a countercurrent extraction by means of hexane butrather a displacement of undesirable hydrocarbons from the ex tractphase and replacement thereof by the hexane.

By way of contrast, when the introduction of secondary furfural isomitted with the other flow rates the same as specified in the table,essentially no separation is effected in column 16 and the materialswithdrawn through lines 19 and 18 have about the same composition as the1st extract phase except for the hexane added.

FIGURE 2 illustrates a modification of the process in which the firstcolumn (not shown) is operated in the same manner as described above butthe second column 20 is operated with a stripping section at the top.The secondary furfural from line 21 is split into two streams with partflowing to the top of the column and the remainder being introducedthrough line 22 into the 1st extract phase which passes through line 23to an intermediate level in column 20. Hexane is fed to the bottomthrough line 25. The amount of furfural introduced through line 22should be at least by volume based on the extract in the 1st extractphase. The portion of the column above line 23 constitutes a strippingsection in which the reject phase is countercurrently contacted with theremainder of the secondary furfural. This type of operation tends togive a still higher recovery of dicyclic aromatic in the 2nd extractphase removed from the base of the column through line 24.

In practicing either of the above-described embodiments, it is preferredto use furfural solvent which contains water and more preferably whichis substantially saturated with water at the temperature of operation.It has been found that the presence of water in the solvent lowers itscapacity for monocyclic aromatics while leaving the capacity fordicyclic aromatics substantially unaffected. Hence the use of water inthe primary and secondary furfural results in obtaining a dicyclicaromatic concentrate of higher purity without reducing the recovery ofdicyclic aromatics. Thus, under conditions comparable to those used forobtaining the data tabulated above but using furfural saturated withwater, the dicyclic aromatic content of the extract product typicallycan be raised from 65% to 75-85% with the recovery of the dicyclicaromatics still being 100%.

Ne claim:

1. Method of preparing an alkylnaphthalene concentrate suitable for hightemperature dealkylation to naphthalene which comprises.

(a) countercurrently extracting a gas oil fraction boiling mainly in therange of 440-515 F. and comprising alkylnapthalenes, monocyclicaromatics and nonaromatics with furfural solvent at a temperature in therange of 10150 F., the ratio of solvent to the total aromatics in thecharge fraction being in the range of 0.75:1 to 7:1 on a volume basis;

( b) separating an extract phase from a rafiinate phase;

(c) diluting the extract phase with furfural solvent in amount of from0.15 to 2.5 volumes of diluent solvent per volume of extract in theextract phase;

(0.) countercurrently contacting the diluted extract phase at atemperature in the range of 10-150 F. with saturated hydrocarbon of theC -C range in amount of 0.5 to 2.0 volumes of said saturated hydrocarbonper volume of extract in the extract phase, whereby said saturatedhydrocarbon mainly dissolves in the diluted extract phase and displacestherefrom non-aromatics and a minor amount of the monocyclic aromaticsto form a reject phase containing said displaced non-aromatics andmonocyclic aromatics and only a minor proportion of said saturatedhydrocarbon;

(e) removing the reject phase;

(f) removing a furfural phase containing most of the alkylnaphthalenesand most of the C C saturated hydrocarbon; and

(g) separating alkylnaphthalene concentrate from said furfural phase.

2. Method according to claim 1 wherein said furfural solvent is furfuralsubstantially saturated with water.

3. Method of preparing an alkylnaphthalene concentrate suitable for hightemperature dealkylation to naphthalene which comprises:

(a) countercurrently extracting a gas oil fraction boiling mainly in therange of 4405 15 F. and comprising alkylnaphthalenes, monocyclicaromatics and non-aromatics with furfural solvents at a temperature inthe range of 70-1 10 F., the ratio of solvent to the total aromatics inthe charge fraction being in the range of 0.75:1 to 2:1 on a volumebasis;

(b) separating an extract phase from a raftinate phase;

(0) diluting the extract phase with furfural solvent in amount of from0.25 to 1.25 volumes of diluent solvent per volume of extract in theextract phase;

(d) countercurrently contacting the diluted extract phase at atemperature in the range of 70-1 10 F. with saturated hydrocarbon of theC -C range in amount of 0.5 to 1.1 volumes of said saturated hydrocarbonper volume of extract in the extract phase, whereby said saturatedhydrocarbon mainly dissolves in the diluted extract phase and displacestherefrom non-aromatics and a minor amount of the monocyclic aromaticsto form a reject phase containing said displaced non-aromatics andmonocyclic aromatics and only a minor proportion of said saturatedhydrocarbon;

(e) removing the reject phase;

(f) removing a furfural phase containing most of the alkylnaphthalenesand most of the C -C saturated hydrocarbon; and

g) separating alkylnaphthalene concentrate from said furfural phase.

4. Method according to claim 3 wherein said furfural solvent is furfuralsubstantially saturated with water.

5. Method according to claim 4 wherein said contacting of the dilutedextract phase with said saturated hydrocarbon is at approximately thesame temperature as said extracting of a gas oil fraction with furfuralsolvent.

6. Method of preparing an alkylnaphthalene concentrate from a crackedgas oil which comprises the steps of (a) countercurrently extracting agas oil fraction boiling mainly in the range of 44-0515 F. andcomprising alkylnaphthalenes, monocyclic aromatics and 5 6 non-aromaticswith furfural solvent at a temperature (1) removing a furfural phasecontaining most of the in the range of 10-150 F., the ratio of solventto alkylnaphthalenes and most of the C -C saturated the total aromaticsin the fraction being in the range hydrocarbon; and of 0.75:1 to 721 ona volume basis; (g) separating alkylnaphthalene concentrate from said(1)) separating an extract phase from a raffinate phase; 5 furfuralphase.

(c) diluting the extract phase with additional furfural 7. Methodaccording to claim 6 wherein said furfural solvent in amount of from0.15 to 2.5 volumes of solvent is furfural substantially saturated withWater. diluent solvent per volume of extract in the extract 8. Methodaccording to claim 6 wherein said extract- P ing temperature is in therange of 70-110" F.

( countercull'ently Contacting the diluted eXtYaPt 10 9. Methodaccording to claim 8 wherein the amount P at appmximately the SametemPerature as m of the C -C saturated hydrocarbon is 0.5 to 1.1 volsaidextracting step, with saturated hydrocarbon of umes the C C range inamount of 0.5 to 2.0 volumes of said saturated hydrocarbon per volume ofex- Ref r c Cit d b th E i tract in the extract phase, whereby saidsaturated 15 hydrocarbon mainly dissolves in the diluted extract UNITEDSTATES PATENTS phase and displaces therefrom non-aromatics and a 10,548/40 Tijmstl'a 208-327 minor amount of the monocyclic aromatics to form2,419,039 4/47 Scarth 208323 a reject phase containing said displacednon-.aro- 2,489,042 1/49 Medcalf et a1. 260-674 matics and monocyclicaromatics and only a minor 20 2,928,788 3/60 Jezl 208-323 proportion ofsaid saturated hydrocarbon; (e) removing the reject phase; ALPHONSO D.SULLIVAN, Primary Examiner.

1. METHOD OF PREPARING AN ALKYLNAPHTHALENE CONCENTRATE SUITABLE FOR HIGHTEMPERATURE DEALKYLATION TO NAPHTHALENE WHICH COMPRISES: (A)COUNTERCURRENTLY EXTRACTING A GAS OIL FRACTION BOILING MAINLY IN THERANGE OF 440-515*F. AND COMPRISING ALKYLNAPHTHALENES, MONOCYCLICAROMATICS AND NONAROMATICS WITH FURFURAL SOLVENT AT A TEMPERATURE IN THERANGE OF 10-150*F., THE RATIO OF SOLVENT TO THE TOTAL AROMATICS IN THECHARGE FRACTION BEING IN THE RANGE OF 0.75:1 TO 7:1 ON A VOLUME BASIS;(B) SEPARATING AN EXTRACT PHASE FROM A RAFFINATE PHASE; (C) DILUTING THEEXTRACT PHASE WITH FURFURAL SOLVENT IN AMOUNT OF FROM 0.15 TO 2.5VOLUMES OF DILUENT SOLVENT PER VOLUME OF EXTRACT IN THE EXTRACT PHASE;(D) COUNTERCURRENTLY CONTACTING THE DILUTED EXTRACT PHASE AT ATEMPERATURE IN THE RANGE OF 10-150*F. WITH SATURATED HYDROCARBON OF THEC5-C8 RANGE IN AMOUNT OF 0.5 TO 2.0 VOLUMES OF SAID SATURATEDHYDROCARBON PER VOLUME OF EXTRACT IN THE EXTRACT PHASE, WHEREBY SAIDSATURATED HYDROCARBON MAINLY DISSOLVES IN THE DILUTED EXTRACT PHASE ANDDISPLACES THEREFROM NON-AROMATICS AND A MINOR AMOUNT OF THE MONOCYCLICAROMATICS TO FORM A REJECT PHASE CONTAINING SAID DISPLACED NON-AROMATICSAND MONOCYCLIC AROMATICS AND ONLY A MINOR PROPORTION OF SAID SATURATEDHYDROCARBON; (E) REMOVING THE REJECT PHASE; (F) REMOVING A FURFURALPHASE CONTAINING MOST OF THE ALKYLNAPHTHALENES AND MOST OF THE C5-C8SATURATED HYDROCARBON; AND (G) SEPARATING ALKYLNAPHTHALENE CONCENTRATEFROM SAID FURFURAL PHASE.